1. Field of the Invention
The present invention relates to a spiral unit having a fin spirally disposed around a longitudinal axis on an outer peripheral surface of a base tube extended along the longitudinal axis. Further, it also relates to an insertion apparatus provided with this spiral unit, and a manufacturing method of this spiral unit.
2. Description of the Related Art
Specification of U.S. Patent Application Publication No. 2012/002981 discloses a spiral unit which is attached to an inserting section of an insertion apparatus, e.g., an endoscope apparatus. This spiral unit includes a base tube extended along a longitudinal axis, and a fin disposed on an outer peripheral surface of the base tube along a fin axis spirally extended around the longitudinal axis. The base tube and the fin are made of a rein. In a state where the spiral unit is attached to the inserting section, the base tube and the fin can rotate together in a periaxial direction of the longitudinal axis with respect to the inserting section. When the base tube and the fin rotate in a state where the fin abuts on a paries portion of a lumen paries or the like, propulsive force in a distal direction or a proximal direction acts on the inserting section.